I have been experiencing the check engine light issue as well. I took my mazda6 to the dealer a few months back due to an emissions recall which they said was causing the check engine light to come on. However it has started to reappear recently. Everytime I reset the gas cap after 8-10 starts it goes out for about 4-5 days then reappears. Has anyone else ever experienced this? Could the gas cap be going bad, I have noticed that it backs off . Also the dealer wants about $40 for a new one, any place to get them a little cheaper?

 

I'd think you could get one at a pick & pull fairly cheap. I wouldn't think they would get damaged in an accident.

 

You did not mention what year your 6 is, but...
03-05 Mazda6 Fuel Cap GM6A-42-250C - retail $16.90
06-08 Mazda6 Fuel Cap GN3E-42-250B - retail $29.76